1. Field of the Invention
The present invention relates to processed pigments, a pigment-dispersed solution, an ink for ink jet, a manufacturing method of processed pigments and a manufacturing method of a pigment-dispersed solution.
2. Description of the Related Art
Dyes and pigments have been conventionally employed as a coloring material in the manufacture of paints, various inks such as a printing ink, an ink for ink-jet and an writing ink, and plastic resins. Pigments are required to be excellent and stable in dispersibility in a solvent component into which pigments are dispersed. Therefore, in order to realize an optimum dispersed state of pigments, various dispersion techniques have been studied to date.
Examples of such dispersion techniques include a method of applying surface treatments to pigments to ensure stable dispersibility, such surface treatments including rosin treatment, surface treatment using a surfactant, treatments using a pigment derivative or treatments using a polymer. For example, there is known a method of manufacturing a carbon black graft polymer wherein carbon black is employed as a pigment and mixed with a polymer having in its molecule 1-2 epoxy group and/or thioepoxy group per molecule at a temperature ranging from 50 to 250° C., thereby allowing a reaction to take place for producing the carbon black graft polymer.
There is also known a method wherein a reactive polymer is employed for enhancing the dispersibility of pigments.
In the case of an ink which is relatively low in viscosity such as an ink for ink-jet, pigments are required to have excellent dispersion properties in order to ensure sufficiently high storage stability and excellent discharge stability of the ink, as well as to secure high quality of printed images. When a large quantity of polymer is employed in the aforementioned method, the viscosity of ink increases, thereby deteriorating the discharge properties of ink, even though the storage stability can be ensured. On the other hand, when pigments are subjected to surface treatment using a surfactant, the storage stability of ink deteriorates. Namely, to date, no one has succeeded in finding a technique which is capable of satisfying all of the requirements involved in the pigment dispersibility.